[dnanian]

Well, in general, Read-Only images spend a lot of time up front ensuring that the image can be written quickly, at a low level, during restore... whereas a read/write image/bundle does a file-by-file copy which takes a longer time. Not much can be done about this, but since you restore rarely and back up frequently, I'd generally advise using a read/write image and paying the rare time price at restore time.